This blog was
originally posted on Cambridge
Wireless on April
1897 the author Mark Twain responded to the premature announcement of his
demise with the now famous quote, “The report of my death was an exaggeration.”
occasion over the last couple of years, some of us working in the passive
antenna business might have been justified in having some sympathy with Mr.
Twain as we were often queried about end of passive antennas in the cellular
market due to the imminent arrival of fully integrated
massive-MIMO solutions in 5G.
However, I can assure you that just like Mark Twain, the death of the passive
antenna has been greatly exaggerated.
active large-scale array antenna systems will have a part to play in the
deployment of 5G NR as they clearly deliver advantages because of their ability
to enable multiuser-MIMO and beamforming which can improve spectral efficiency
and capacity within a given area. If 5G was being implemented as a “greenfield”
network, it might be reasonable to design the RAN infrastructure to support a
large proportion of such active antennas in a cost-effective way. However, in
virtually all networks, certainly in developed markets, this is not the case
and 5G will have to be layered on top of legacy 2G, 3G and 4G networks using
infrastructure such as towers and power delivery systems which have possibly
been in the field for over 10 years and were not designed to support the level of
tower-top equipment now being deployed.
CLICK TO TWEET: Colin Bryce explains that just like Mark Twain, the death of the passive antenna has been greatly exaggerated.
operators want to initially deploy 5G onto their existing network of macro cell
sites which may already host several antennas on each sector. Adding additional
antennas to such sites is not always straightforward. A few factors to consider:
- Will legacy infrastructure support the
additional weight and wind loading?
- Will local zoning/planning permit an
- Will landlords allow an additional antenna
(or use the opportunity to renegotiate leasehold agreements)?
these types of issues exist at a site, then traditional passive antenna
technology can come to the rescue.
antenna technology has evolved significantly over the last few years and modern
passive antennas can support multi-band, multi-RAT systems from within a single
radome. In 2010, a typical high-end antenna would support perhaps 10 jumper
ports, but now this has increased to 26 and even 30 ports. In addition, the
linear array columns in the antenna are wide band and only two column types
(low-band and high-band) can support all deployed frequencies from the 700MHz
band through to 2.6GHz. This makes it possible to combine all existing cellular
technologies on a site into three passive antennas (one per sector) while still
supporting independent remote electrical tilt (RET) for each band. These
antennas also support 2T2R or 4T4R architectures to continue to deliver
diversity or MIMO capability.
is important as it can allow operators to deploy a separate independent 3.5GHz
active antenna on sectors that have consolidated all their legacy networks onto
a single passive antenna. Two antennas per sector are more likely to be
permitted on a significant proportion of sites and also limits the landlords
leverage in any negotiation of site fees as the operator is not requesting an
increase in the number of antennas on the site.
has gone even one stage further; by designing a complementary radome that
seamlessly mounts on top of a standard antenna to look like one unit. This
additional radome can be used to enable the operator to apply for site
permission for a single antenna but the space can be used to upgrade the site
with a m-MIMO antenna or passive beamformer as and when needed.
antennas will not only be used to serve legacy technologies but will also play
a part directly in the roll out of 5G NR in the 3.5GHz bands. While we have
discussed the potential capacity and spectral efficiency of active antennas, as
with all technologies there are drawbacks. We have already mentioned weight and
wind load. However, some other aspects that should be considered when selecting
antennas might include:
- Can power be economically delivered to the
- Is the exact location of mounting antennas
going to limit RF coverage?
- Will the pattern of UE distribution across
the cell enable full spatial diversity gains?
- Are there any EMF emission restrains that
will limit beamforming benefits?
- Is there a need to share the site with
other operators and if so will the site support more than one active antenna
- Are any capacity gains justifiable in
terms of the costs involved in deploying active antennas?
in mind that only a small percentage of sites in most networks are nearing
capacity limitations. Many regulators in Europe are packaging 3.5GHz into
spectrum blocks of around 75MHz which is of a similar order of bandwidth to
that currently used in downlink legacy FDD. If an additional 15 to 20 percent
of spectral efficiency improvement provided by 5G NR is considered, then
operators can deploy 5G NR at much lower costs using a passive beamforming
antenna along with an 8T8R (or even 16T16R in future) RU and still benefit from
significant capacity increase as well as other 5G benefits.
as 5G networks are being rolled-out, the market for large port count passive
antennas will increase dramatically and in addition, a significant portion of
5G is likely to be deployed on sites using passive beamforming antennas. There’s
life in the old passive antenna yet.
you want to learn more, I encourage you to join me during the Cambridge
Wireless Conference “5G
wide area coverage: macro cells – the why and the how” on May 9. We
will explore the design and optimization of the macro cell layer and its role
within the future heterogeneous networks.